This application claims the benefit of Korean Application No. 2001-74292, filed Nov. 27, 2001, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a microwave oven having a magnetron which oscillates high-frequency electromagnetic waves and a device which distributes the high-frequency electromagnetic waves through a cooking cavity and, more particularly, to a microwave oven which limits a rotation trace range of a wave distributing device.
2. Description of the Related Art
In general, a microwave oven is an electrically operated oven which radiates high-frequency electromagnetic waves (of about 2450 MHz), generated by the oscillation of a magnetron, through a cooking cavity. In the cooking cavity, the high-frequency electromagnetic waves, so-called xe2x80x9cmicrowaves,xe2x80x9d penetrate food and cause its molecules to vibrate and generate heat to cook the food. Such a microwave oven is provided with a device which distributes the microwaves through the cooking cavity.
FIG. 1 shows a conventional microwave oven having a wave distributing device. The wave distributing device comprises a metal stirrer fan 4 which is installed at a top portion of an cooking cavity 3 of an oven body 1 and is operated by a motor 5. Generally, the motor 5 is started simultaneously with the start of a magnetron 2, and rotates the stirrer fan 4 to distribute microwaves, which are radiated from the magnetron 2, through the cooking cavity 3 to heat and cook food laid on a cooking tray 6 of the cooking cavity 3.
FIG. 2 shows another conventional microwave oven having a different type of a wave distributing device. The wave distributing device of the microwave oven shown in FIG. 2 comprises a metal antenna 7 which is installed at a top portion of a cooking cavity 3 of an oven body 1 and is operated by a motor 5. Generally, the motor 5 is started simultaneously with the start of a magnetron 2, and rotates the antenna 7 to distribute microwaves generated from the magnetron 5 through the cooking cavity 3.
As described above, the wave distributing devices of conventional microwave ovens either rotate the stirrer fan 4 or the antenna 7 using the motor 5, which is simultaneously started with the start of the magnetron 2, to distribute the microwaves through the cooking cavity 3.
Intrinsic impedance characteristics of microwave ovens are, in part, determined by the types of wave distributing devices used in the microwave ovens. To improve an energy efficiency of the microwave ovens, it is necessary to optimize the impedance characteristics of the microwave ovens. Therefore, an impedance matching must be carried out during a process of designing a microwave oven. That is, impedance characteristics of a microwave oven are measured using, for example, a network analyzer and an antenna probe on Rieke charts to design the microwave oven having the maximum energy efficiency.
FIG. 3 shows a Rieke chart illustrating a distribution of impedance characteristics of a conventional microwave oven. The impedance characteristics were measured under a standard load (water of 1000 cc). In this drawing, it is noted that the impedance of the microwave oven has been matched to obtain the maximum energy efficiency.
However, FIG. 4 shows that even though the conventional microwave oven is designed to match its impedance under the standard load, the impedance characteristics of the microwave oven under a no-load or a light load are distributed differently from the distribution characteristics corresponding to the standard load. That is, FIG. 4 shows that the impedance characteristics of the conventional microwave oven are distributed at an outside area of the Rieke chart. Accordingly, the maximum energy efficiency is not achieved and the life expectancy of the magnetron 2 is reduced. In other words, the magnetron 2 of the conventional microwave ovens are prone to overheating because under a no-load or a light load, the microwaves distributed by the metal stirrer fan 4 or the metal antenna 7 are returned to the magnetron 2 due to a reduction in the amount of load absorbing the microwaves. With the magnetron 2 overheated, operational reliability and safety of the conventional microwave ovens are reduced.
Therefore, there is a need to design a microwave oven having impedance characteristics that are not distributed at an outside area of the Rieke chart even where a magnetron is started under a no-load or a light load. However, it is noted that a distribution of intrinsic impedance characteristics of a microwave oven is difficult to control because the intrinsic impedance characteristics change in accordance with the structure, shape and material of a cooking cavity of the microwave oven.
In accordance with experiments performed by the inventor of this invention, impedance characteristics of a microwave oven are differentiated in accordance with a rotation trace of a stirrer fan or an antenna. Thus, it is possible to divide the entire range of the rotation trace of the stirrer fan or the antenna into a section resulting in a good distribution of the impedance characteristics, and into another section resulting in a bad distribution of the impedance characteristics. As described above, the intrinsic impedance characteristics of a microwave oven changes in accordance with the structure, shape and material of a cooking cavity. Accordingly, a range of the rotation trace of the stirrer fan or the antenna resulting in a good distribution of the impedance characteristics is changed in accordance with a model of a microwave oven.
Therefore, it is possible to improve the impedance characteristics of a microwave oven because the rotation trace of the stirrer fan or the antenna is limited to a predetermined range on the basis of data obtained during the process of designing the microwave oven. Particularly, such a limited rotation trace desirably improves the impedance characteristics of the microwave oven under a no-load or a light load.
Accordingly, it is an object of the present invention to provide a microwave oven having a wave distributing device which is designed to optimize intrinsic impedance characteristics of the microwave oven, thus improving the energy efficiency and the operational reliability of the microwave oven.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects of the present invention, there is provided a microwave oven comprising a cooking cavity, a magnetron which generates high-frequency electromagnetic waves, a wave distributing device which distributes the high-frequency electromagnetic waves through the cooking cavity, wherein the wave distributing device comprises a rotor which is installed inside the cooking cavity and distributes the high-frequency electromagnetic waves through the cooking cavity, a rotation trace limiter which limits a rotation trace range of the rotor, and a motor which reversibly rotates the rotor.
According to an aspect of the present invention, the rotation trace limiter comprises a stopper which limits a rotation of the rotor. The stopper may comprise a cylindrical rod, where one end thereof is fixed to a corresponding area of the rotor. The stopper may comprise a core member and an elastic member which covers the core member.
According to another aspect of the present invention, the rotation trace limiter comprises a cam mechanism unit which changes a movement of a motor shaft that connects the rotor to the motor.
According to yet another aspect of the present invention, at least two stoppers are used in the wave distributing device to limit the rotation of the rotor to the rotation trace range.
According to still another aspect of the present invention, the motor is a synchronous motor which is rotated in a forward direction or a reverse direction by an alternating current. The synchronous motor reciprocates the rotor within the rotation trace range. The synchronous motor is rotated in the forward direction to rotate the rotor in one direction, and is rotated in the reverse direction to rotate the rotor in the opposite direction in response to a contact between the rotor rotated in the one direction with the stopper.
The rotation trace range limited by the microwave oven of the present invention provides low intrinsic impedance characteristics as compared to conventional microwave ovens having an unlimited rotation trace range which results in poor impedance characteristics.